Pressed paperboard containers, including plates, bowls, platters, etc., with any appreciable vertical draw generally have some form of material gathering in the drawn regions, usually depicted as a structure commonly called pleats. The pleats are located around the periphery of a container, in areas in which the vertical drawn portion follows a curved path about the periphery.
During the manufacturing process of forming the container, a process referenced herein as “conversion” of the paperboard blank into a container, the paperboard stock at the outer regions of blank fold to accommodate the excess material gathering at regions where the vertical draw follows such a curved path. As the conversion process continues, mating dies that are used to form the depth or draw of the container move toward each other, and are typically configured as mating dies with little or nominal die clearance between the mating surfaces. In this manner, the mating conversion dies act on each folded segment of paperboard in the outer regions of the container to create formed pleats. As is well known in the art, tightly packed and ironed out pleats, and preferably ones with at least some degree of bonding of pleat layers or integration and re-bonding of the layers of paperboard fibrous material, will provide resistance from separation of the pleat layers when the container is in use.
Thus, one of the ways to improve the appearance and the rigidity of a formed paperboard container it to provide generally inseparable pleats in normal-use conditions, resulting in greater resistance from deformation of the container such as when a load of food items are placed on the container. Further, it is known that poorly formed pleats will result in an unattractive appearance, and regions of delaminated paperboard that act as lines of weakness for possible catastrophic buckling of the paperboard container, sometimes even when the user places a normal load (amount of food) on the container. Thus, prior attempts at increasing plate rigidity have focused on applying increased heat and pressure by the dies to iron out the pleats.
Prior art paperboard plates generally have either randomly-formed pleats, or radially-extending linear pleats that are formed by scoring along a radial line. Such scored pleats are formed in a desired pattern or arrangement by scoring the blank between dies prior to converting the container into its drawn shape. Scoring weakens the material at the points of scoring by damaging the laminar structure of the paperboard, which influences the paper to fold at the scored areas when the paperboard is pressed into a container, such as a plate. Thus, scoring of paperboard prior to converting the plate results in a catastrophic de-lamination of the paperboard in the scored regions, which causes a loss of integrity of the rigid paperboard.
Prior art containers with scored pleats are made with linear pleats formed of linear scores in the blank, and pleats/scores extend radially outward relative the center of the plate. Thus, such pleats common to prior art plates and processes may be described as “linear” along their length, and “radial” as they extend along a radial line across the diameter of the container. Similarly, therefore, such pleats are created by first forming scores in the paperboard blank, wherein such scores are linear along their entire length and extend radially outward along a respective radial line across the diameter of the blank. Such common structure and method of pleated paperboard containers is described in numerous patents, including the following: U.S. Pat. Nos. 4,609,140; 4,606,496; 4,721,499; 5,938,112; and, 7,048,176.
Prior art scored pleats are formed in the shape of the linear radial score. If there is no scoring of the blank for pleats, then randomly-formed pleats result as the paperboard blank is converted into a depth by forming dies. Such randomly formed pleats then naturally form in unspecified arrangements around the outer regions of the container. Randomly-formed pleats often have a linear length and reside along a radially extending line of the container. Randomly formed non-scored pleats may also include non-linear portions of the pleats and portions that do not extend along a radial line. As is known in the art, random non-scored pleats are not desirable, as the uncontrolled pleat formation causes inconsistencies and generally inferior pleats.
Non-scored randomly-formed pleats are not desired due to being less attractive in appearance and non-uniformity of pleats along the outer region of the container. The poor formation of such pleats is due in part to the natural occurrence of an uncontrolled amount of paperboard material gathered into a pleat, simply due to a lack of scoring that would be needed to provide weakened paperboard regions to direct and disperse the “gathering” of paperboard. Similarly, the lack of such score arrangement results in the randomly-formed pleats having undesirable variation in the orientation and/or frequency of such pleats.
Although scoring the blanks for pleat formation, and forming such scored pleats in finished paperboard containers is advantageous and desirable for numerous reasons as described above, such pleats may result in a linear path of weakened paperboard susceptible to creasing or folding when the container is in use and is subject to a load or distortion by being carried by the user. For example, when a container, such as a paper plate, is subject to a heavy load of food and is held by a user in a manner that potentially distorts a region of the plate, the pleat may then act as a line of weakness of the rigidity of the paperboard. The result, of course is that the plate folds along the line of weakness of the pleat, which may be even more likely as the hinge-line of the fold reaches a similar radially extending pleat on the other side of the plate.
Further, linear and/or radial-extending pleats are believed to be susceptible to separation of pleat layers when subject to the compressive and tensile stresses in use, such as when food is loaded on a plate. This is believed to be primarily due to the linear and radial path of the pleat, such that separation of the paperboard propagates along a directly linear path of the radial pleat.
As an example of such features and problems in the prior art, a prior art circular paperboard container (1) is shown in FIGS. 1-2, having a bottom wall 2 with an annular recessing 3 encircling the bottom wall 2, an upturned sidewall 4 extending upward from the bottom wall 2, a relatively flat rim 5 extending outwardly from the sidewall 4, and a downturned lip 6 extending downward from the rim 5 to the edge of the plate 1.
As shown in FIGS. 1 and 2, a plurality of pleats 7 are located around the peripheral region of the container. The pleat typically extends from an area in the sidewall 4, and extends radially outward through the rim 5 and the lip 6 and to the outer edge of the container. The pleats 7 of the container shown in FIGS. 1-2 are linear and each aligned along a respective radially extending axis A-A. This is depicting what is being described as both “linear” and “radially extending” pleats, residing along a cross sectional line of the container diameter.
A alternative specific geometry of the plate structure is common. For example, prior art container geometry may not include a recess ring 3 around the bottom wall 2, and may have a curved or rounded rim 5, rather than a flat or substantially horizontal portions of the rim 5. Still other paperboard designs are elliptical, obround, or rectangular in shape rather than substantially round. In such non-circular containers, pleats generally form where the container has curvature in the well or drawn region. Thus, much like the linear and radially extending pleats shown in FIGS. 1-2, non-round containers typically include pleats that are linear, and reside along a radially extending line relative the radial line of the curved segment of the container.
Also, the method of manufacturing plates after forming a scored blank are well accepted and common. Paperboard containers are formed from a blank cut from paperboard sheet stock. Typically, the score lines are formed as the blank is cut from the sheet. Thus it is known that the containers must be formed by pressure exerted between mating manufacturing (“conversion”) dies, while preferably optimizing the moisture content of the paperboard and subjecting the paperboard to heat and pressure from the dies to facilitate pleat forming. A prior art circular blank 8 is shown in FIG. 3, such as would be suitable for forming the paperboard plate container of FIGS. 1 and 2, when drawn into the shape shown in the cross-section view of FIG. 4. A plurality of non-segmented radial, linear score lines 9 are located around the edges of the blank 8, which are designed to form the radial, linear pleats 7 in the plate of FIGS. 1-2. thus, the scores 9 formed in the manner of the prior art are formed as thin bands of disrupted or delaminated paperboard that have score lengths that are linear and which extend radially outward relative a cross sectional line B-B of the diameter of the paperboard blank.
Other shapes and sizes of blanks are used to create other types of prior art containers, and these prior art blanks may be scored as desired. In sharply curved areas of the blank and smaller round plates or similar containers, where pleats form close to one another, scoring is usually closely spaced. Regardless of the number or arrangement of score lines in such prior art containers, however, linear radial scores result in radial linear pleats in the container 1. Such pleats are subject to susceptibility to separate along the linear pleat path. Further, the general alignment of opposed straight pleats at opposite edges of the plate is susceptible of forming a crease line across the width of the container, resulting in buckle failure of the structure. Thus, there is a need for an improved paperboard container structure, and method for manufacturing the same, which has increased rigidity and optimized gathering of pleated material.
The present invention is provided to solve the problems discussed above and other problems, and to provide advantages and aspects not provided by prior containers of this type. A full discussion of the features and advantages of the present invention is deferred to the following detailed description, which proceeds with reference to the accompanying drawings.